Cusco
announced it would be producing LSD's for the Z. I'm sure more will be available in the future.
So to answer your question, "will you be able to add an LSD to the car" I'm pretty sure you CAN... but its most likely going to cost you more than the sports package to buy a LSD and brakes + installation. But if the stock LSD and brakes aren't going to fit your needs then by all means look at aftermarket options.